[RFC] Enabling -flto in libstdc++?

[Joseph S. Myers]

On Tue, 20 Oct 2009, Diego Novillo wrote:

> On my nightly tester I force libstdc++ to be built with -flto enabled using
> 
> $ make check RUNTESTFLAGS=--target_board=unix/"\{-flto/-O2,-fwhopr/-O2\}"
> 
> Recently, this started showing 17 regressions that we don't see in
> other testsuites.  It would be useful if we would run libstdc++ with
> -flto as well as the regular options.  This will make testing
> libstdc++ longer, but it is useful for LTO as several of these tests
> are significant.
> 
> Would this be OK?

libstdc++ is a very slow testsuite to run (compared with g++, for 
example), at least if your target board is slow.  There are infinitely 
many combinations of tests you could run; that a combination is useful 
does not mean it is appropriate to increase default testing time for 
everyone with it.  Instead, different people should run regression testers 
with different options and report bugs found to Bugzilla; just as some 
people run the testsuites with -fpic/-fPIC, or have processes for 
generating testcases likely to trigger bugs and then report those bugs, 
you could do run such a tester with LTO options and report the bugs you 
find.  Diversity of testers, and people actually going through the results 
and ensuring there are PRs for all existing or new failures and that 
regressions are marked as such, is more worthwhile than duplication of 
similarly configured testers.

-- 
Joseph S. Myers
joseph@codesourcery.com